(a) Field of the Invention
The present invention relates to a system and a method for electrolytic plating and, more particularly, to a technique for forming a metallic film on a semiconductor wafer by using an electrolytic plating technique with a magnetic field.
(b) Description of the Related Art
Aluminum (Al) generally used for wiring between semiconductor elements in an LSI is to be replaced by copper (Cu) in view of the lower electric resistance of the latter. An electrolytic plating technique is known as a method for forming a Cu film on a wafer, wherein Cu ions are deposited on the subject surface of the wafer by conducting current through an aqueous solution of electrolytic substance including Cu ions to the wafer for deposition of the Cu ions.
In fabrication of the LSI, it is important that the Cu film has a uniform thickness on the subject surface of the wafer. However, the electrolytic plating technique generally incurs a problem in that a thicker Cu film is formed on the peripheral area of the wafer compared to the central area thereof. To solve this problem in the current electrolytic plating technique, the electrolytic solution is stirred by a stirrer or added with additives for obtaining a uniform thickness for the Cu film.
The technique for stirring the electrolytic solution incurs the ingress of contaminants or contaminating substances through the stirrer, whereas the technique using the additives also involves attachment of contaminants to the wafer. The stirring technique in fact does not afford a sufficient uniformity in the thickness of the resultant film because the stirring itself cannot accurately control the flow of the electrolytic solution.
In addition, an ununiform current density occurs along the resistance distribution of subject surface of the wafer, which also incurs the uneven thickness of the resultant film. In particular, in the case of a lower resistivity of the wafer, a higher concentration of dopant is introduced in the semiconductor substrate. This increases the variance in the resistivity and thus degrades the uniformity of the resistivity distribution, whereby a uniform thickness is difficult to achieve.
In view of the above, it is an object of the present invention to provide a system and a method for electrolytic plating on the surface of a wafer with a uniform thickness.
The present invention provides a method for electrolytic plating on a subject surface of a wafer including the steps of contacting a subject surface of a wafer with electrolytic solution, applying a DC voltage between the wafer and the electrolytic solution while applying a magnetic field in the electrolytic solution.
In accordance with the method of the present invention, the magnetic field applied to the current components which are perpendicular to the magnetic field stirs the electrolytic solution to obtain a uniform distribution of ions of the electrolytic substance in the electrolytic solution without using a stirrer, thereby preventing the ingress of the contaminants. In addition, the magnetic field strength can be controlled with ease by controlling the applied voltage, which effectively preventing the ununiform thickness of the resultant film.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.